Wireless frequencies are regulated by government agencies. In the U.S., for example, the Federal Communications Commission (FCC), among other duties, is responsible for regulating the use of the wireless spectrum. Increasingly, it has become desirable to make more efficient use of spectrum. Efforts to facilitate maximum utilization of spectrum have resulted in ongoing innovation.
For a spectrum that is allocated for use by a particular user (a primary user) it is possible for another user (a secondary user) to operate within the same spectrum as long as the secondary user does not interfere with the primary user. There are various technical difficulties in accomplishing the goal of enabling secondary users to make use of “unused” bandwidth. Problems include detecting the presence of a primary user before attempting to utilize wireless resources, making way for the primary user if one is detected, and providing other wireless resources if a secondary user has to make way for a primary user. Parameters for accomplishing these goals can vary with the nature of the primary user, regulations, characteristics of a particular channel, and other factors.